Yes, it does have hydraulic fluid in them - thus making them "hydraulic". If you get a leak, you'll lose pressure and breaking power and eventually get nil, but I have not heard many hydro users complain of leaks so I would assume they are sturdy systems (I don't use them). It can freeze up in the winter, but at about the same temperatures car break fluid would freeze at, so you should be fine unless you are in the extreme cold, probably negatives.